Apparatus for heating dielectric materials electronically



March 15, 1949. H. c. GILLESPIE 2,464,404

APPARATUS FOR HEATING DIELECTRIC MATERIALS ELECTRONICALLY Filed Sept.28, 1945 v MIA/W! 1110M? ELECTRODES IN VEN TOR.

ATTORNEY Patented Mar. 15, 1949 UNITED STATES APPARATUS FOR HEATINGDIELECTRIC MATERIALS ELECTRONICALLY Henderson 0. Gillespie, Moorestown,N. 1., assignor to Radio Corporation of America, a corporation ofDelaware Application September 28, 1945, Serial No. 619,177

12 Claims. 1

This invention relates to apparatus for heating dielectric materialselectronically, and more particularly to the heating of moisture ladendielectric articles to expel moisture therefrom, the present inventionbeing in the nature of an improvement over that disclosed and claimed inthe copending application of George W. Klingaman, Serial No. 613,508,filed August 30, 1945, and assigned to Radio Corporation of America.

In the course of manufacturing various articles of dielectric materials,it is frequently necessary to subject the articles to a washingoperation during which they are, of course,-rendered wet. Thus, in thecourse of producing rayon thread, artificial sponges, and similararticles of cellulosic materials, one or more washing operations may beencountered. It then becomes necessary to expel the moisture from sucharticles, since they are eventually supplied to the market or areutilized in the dry or substantially dry state.

In the manufacture of rayon thread or yarn, for example, it has beenproposed heretofore to dry the so-called wet rayon cakes or packages bysubjecting them to the influence of a high frequency electric field.Rayon and many other dielectric materials which are capable of absorbingmoisture have the characteristic that the power factors thereof vary asa function of the moisture content. Thus, as the rayon cakes or packagesare dried, the power factor thereof changes and, for a given voltagewhich is applied to the work, a point is reached sooner or later whereit becomes very difficult to put enough power into the work to continuethe drying process at an adequate rate.

In the above identified copending application of Klingaman, there isdisclosed a novel electrode system for heating dielectric articles ofthe character under consideration in a manner to apply greater voltageto the articles at a certain point in the heating cycle. The Klingamanarrangement involves the use of a heating unit comprised essentially ofan inductor constituted by a pair of elongated, opposed electrodesspaced from each other to receive therebetween the articles to be heatedand having an inductor connected thereacross in proximity to the inletend thereof. To tune the circuit, there is provided a variable capacitorwhich is connected across the other end of the aforementionedelectrodes. At a point intermediate the ends of the inductor electrodes,a second inductor is connected across the electrodes. With thisarrangement, the voltage across the electrode portions between the inletend thereof and the point at which the last mentioned inductor isconnected thereto will vary at a relatively low rate sufficient to expelmost of the moisture from the wet articles. By the time the articleshave been advanced to the 5 point where the last mentioned inductor isconnected across the electrodes, the articles will have had aconsiderable part of the moisture expelled therefrom and the powerfactor thereof will have changed considerably so that the effectivenessof the field must be increased from that point on. In the arrangementproposed by Klingaman, the voltage from the last mentioned point on tothe outlet end of the electrodes will increase at a much higher rate,and therefore i more power will be applied to the work for a unitdistance along which the work is advanced. By the time the work willhave reached the outlet end of the electrodes, it will have attained aminimum moisture content and will have become as dry as may be desired.

' While the system proposed by Klingaman affords very satisfactoryresults, it has the disadvantage that the total power drawn from thegenerator is increased by reason of the fact that the tuning capacitoris added to the inductor electrode unit. Thus, the efliciency ofKlingaman's system is not as great as might be attained. The primaryobject of my present invention is to provide an improved apparatus forheating 3o dielectric articles the power factors of which changeappreciably during the heating process,

I which apparatus will not be subject to the aforementioned limitationof the Klingaman system.

More particularly, it is an object of my present invention to provide animproved apparatus for heating wet dielectric articles whichwill'effectively' carry out the drying operation in a highly emcientmanner.

Another object of my present invention is to 40 provide, in heatingapparatus of the type set forth above, an eflicient and flexibleelectrode tuning arrangement where a variable voltage along the lengthof the electrodes is required.

7 It is also an object of my present invention to provide improvedheating apparatus as aforesaid in which the heating of dielectricarticles may be effected rapidly and in great quantities, which willdraw a minimum of power from the generator, and which is highlyeiiicient in use.

In accordance with my present invention, I sectionalize the longelectrodes such as are used in conjunction with a conveyor belt in adielectric heating application of the type set forth above, and connectthe sections in such a manner as to 55 provide both the capacitive andthe inductive tuning elements needed in the load circuit. One way ofaccomplishing this, for example, is to split one bf the electrodes intotwo parts each of which has a length which is less than one-quarter wavelength at the operating frequency and to serially connect these twoelectrode parts by a suitable impedance element, such as a variableinductor. Further, in accordance with my invention, I connect aninductor across one of the electrode sections, preferably at the endwhere the wet articles are introduced. This inductor is of such valuethat it makes an inductance out of this particular electrode section atthe operating frequency. The other electrode section may be left open atboth ends whereby it constitutes a capacitive section. By suitablechoice of constants, resonance can be obtained between the inductive andthe capacitive sections of the electrodes without the necessity ofproviding an additional tuning capacitor as in the Klingaman system. The

4 inductor which connects the two electrode sections is also useful inadjusting the resonant frequency of the combination and is effective inobtaining an increased voltage rise along the electrodes at the pointwhere, in the course of travel of the work along the electrodes, it isfound neeessary to increase the voltage. With a system of this sort, thetotal load circuit kva. are not increased, as in the case of theKlingaman system, since no capacitive reactance is added to theessentially capacitive load.

The invention, together with additional ob-- jects and advantagesthereof, will be better understood .by reference to the accompanyingdrawing, in which Figure 1 is a diagrammatic view of one form of heatingapparatus according to my present invention, and

Figure 2 is a curve showing the voltage distribution along theelectrodes of Fig. 1.

Referring more particularly to the drawing, there is shown an elongated,conductive member I which may be connected to ground and whichconstitutes a first electrode disposed in one plane,

and two additional electrodes 3 and 5 spaced from each other anddisposed in a common plane above the electrode l. Thus, there areprovided two electrode sections i, 3 and l, 5 between the respectivepairs of electrodes of which the dielectric articles I (such as wetrayon cakes or the like) are received in energy transfer relation withrespect thereto. Each of the electrode sections I, 3 and l, 5 has alength which is less than onequarter wave length at the operatingfrequency. The articles 1 are advanced by an endless belt 9 of canvas orthe like which is trained around the pulleys ll, one of which may bedriven by a motor l3. I

Connected across the electrodes i and 3 in proximity to the electrodesection l, 3 is a variable inductor l5 which is preferably madeadjustable along the length of the electrode section I'. 3, butnotnecessarily so. By connecting the inductor l5 across the section I,3, this section becomes essentially an inductive section L. Theelectrode section I, 5 is open at both ends and, since the electrode 5is capacitively related to the electrode I, the section I, 5 constitutesa capacitive section C. The inductive section L and the capacitivesection C may be tuned to resonance at the operating frequency of a highfrequency oscillation generator H (such as a vacuum tube oscillatoroperating at radio frequency) without the use of any additionalcapacitors. The electrodes 3 and 5 are serially connected at theirproximate ends by a suitable impedance element, such as a variableinductor [9. The inductor i9 is also useful in adjusting the resonantfrequency of the combination. Connection between the generator I! andthe electrode system is preferably made by means of a concentrictransmission line 2| the outer conductor 23 of which is preferablyconnected to ground and the inner conductor 25 of which may be connectedto the junction of the electrode 3 and the inductor IS.

The fresh, moisture laden articles I are introduced into the heatingapparatus at the left hand end of the inductive section L and areadvanced successively first through the section L between its electrodesI and 3 and then through the section C between its electrodes 1 and 5.The voltage distribution along the inductive electrode section L fromthe entrance end thereof to the exit end thereof is represented by thecurve W-X of Figure 2, while the voltage distribution along thecapacitive electrode section C from the point AA to the exit end thereofis shown by the curve Y--Z of Figure 2. From the entrance end of theinductive section L to the exit endthereof the wet articles I aregradually dried until, at the point A--A, sufflcient moisture has been'expelled therefrom to make further heating dimcult at the voltage X byreason of the decreased power factor of the .partly dried articles.However, the inductor l9 causes the voltage to rise sharply at the pointA-A from the value X to the value Y, so that, from the point A-A on, 'a

much higher voltage is applied to the work and therefore more power canbe put into the partly dried articles I until, at the exit end of theelectrode system, the articles 1 have reached the desired state ofdryness.

It will be apparent, from the foregoing description, that a minimumamount of power is drawn from the generator it since no additionaltuning elements are required in the heating circuit other than theelectrodesections L and C. It will also be apparent that the presentinvention, although described with special reference to the drying ofmoisture laden, dielectrlc'artieles, is broadly applicable to thegeneral heating of dielectric articles (whether wet or dry) the powerfactors of which change materially during the heating operation. It mayalso be pointed out that, with an arrangement such as described above,it has been possible to obtain a desired voltage distribution along theelectrode system with none of the articles fl or other material inprogress through the electrode system. Under this no-load condition,practically no power is drawn from the generator until the material tobe heated enters the heater. If the articles I or the like are then fedin through the successive electrode sections L and C, as abovedescribed, the

amount of power delivered by the generator will automatically increaseproportionally to the amount of work between the electrodes. until theelectrode system is full, when full power will be delivered. During thisprocess, the desired electrode voltages are maintained.

Although I have shown and described but a single embodiment of myinvention, it will undoubtedly be apparent to those skilled in the artthat many variations thereof are possible. For example, instead ofmaking the electrode I of a single, elongated, conductive member, it maybe made of two, separate members one associated with the electrode 3 andone with the electrode 5 and each of said separate members groundedsimilarly to the electrode i. Also, in place of the inductor l9, anyother suitable impedance element, such as a capacitor or resistor, orany suitable combination of inductors, capacitors and/or resistors, maybe employed, depending upon the constants of the system and the voltagedistribution that may be desired. Various other changes will, no doubt,readily suggest themselves to those skilled in the art. Hence, I do notintend to be limited merely to the precise arrangement disclosed herein.Y

I claim as my invention:

1. Electrical heating apparatus for heating dielectric articlescomprising an alternating current circuit having a section which isinductive and a section which is capacitive at a predetermined operatingfrequency, each of said sections including a pair of conductive memberswhich are spaced from each other to receive said articles therebetweenin energy transfer relationwith respect thereto, impedance meansserially connecting said sections, and power input means for couplingsaid circuit through said inductive section substantially at theconnection therewith of said impedance means to a source of alternatingcurrent at said operating frequency.

2. Electrical heating apparatus for heating dielectric articlescomprising an alternating current circuit having a section which isinductive and a section which is capacitive at a predetermined operatingfrequency, each of said sections including a pair of conductive memberswhich are spaced from each other to receive said articles therebetweenin energy transfer relation with respect thereto, one of said conductivemembers being common to each of said pairs, an inductor seriallyconnecting the two other conductive members of said pairs, and powerinput means for coupling said circuit to a source of alternating currentat said operating frequency, said power input means providing couplingwith the common one of said conductive members and with the inductivesection substantially at the Junction with said inductor.

3. Electrical heating apparatus for heating dielectric articlescomprising a circuit tuned to resonance at a predetermined operatingfrequency, said circuit including a pair of elongated sections arrangedsubstantially in end to end relation and each including a pair ofconductive members which are spaced from each other to receive saidarticles therebetween in energy transfer relation with respect thereto,a first inductor connected across the pair of members of one of saidsections whereby to constitute said one section an inductive section atsaid operating frequency, the other of said sections being open at itsends and constituting a capacitive section at said operating frequency,a second inductor serially connecting said sections, and power inputmeans for coupling said circuit to a source of alternating current atsaid operating frequency, said last named means providing an inputconnection with one conductive member of each section and another inputconnection with the inductive section substantially at the connectiontherewith of said second inductor.

4. Electrical heating apparatus according to claim 3 wherein said firstinductor is connected across the conductive members of said one sectionin proximity to that end thereof which is remote from said othersection.

5. Electrical heating apparatus according to claim 3 wherein said firstinductor is adjustable along the length of said one section.

6. Electrical heating apparatus according to claim 3 wherein saidinductors are both variable.

7. Electrical heating apparatus according to claim 3 wherein one of saidconductive members is common to each of said sections.

8. Electrical heating apparatus employing alternatlng current forheating dielectric articles which comprises a circuit tuned to resonanceat a predetermined operating frequency, said circuit including a firstand elongated conductive memher, second and third conductive membersspaced from said first member to receive said articles therebetween inenergy transfer relation with respect thereto, said third conductivemember being also spaced from said second conductive member, a firstinductor connected across said first and second members, a secondinductor serially connecting said second and third members, and powerinput means for coupling said circuit to a source of alternating currentat said operating frequency, said last named means providing a powerinput connection to said first conductive member and to said secondconductive member substantially at the Junction therewith of said secondinductor.

9. Electrical heating apparatus according to claim 8 wherein said firstnamed, elongated, conductive member is disposed in one plane, andwherein said second and third conductive members are disposed in acommon, second plane spaced from said first plane,

10. Electrical heating apparatus according to claim 1 characterized inthat said sections are disposed successively along a certain path, andcharacterized further by the addition of conveyor means disposed alongsaid path between the conductive members of each of said sections forreceiving thereon the articles to be heated and for advancing saidarticles successively through said sections.

11. Electrical heating apparatus according to claim 1 characterized inthat said sections are disposed successively along a certain path, andcharacterized further by the addition of conveyor means disposed alongsaid path between the conductive members of each of said sections forreceiving thereon the articles to be heated and for advancing saidarticles successively first through said inductive section and thenthrough said capacitive section.

12. Electrical heating apparatus according to claim 8 wherein said meansfor coupling said tuned circuit tosaid source comprises a concentrictransmission line of which the inner conductor is connected to saidcircuit at said junction of said second conductive member and saidsecond inductor.

HENDERSON C. GILLESPIE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,972,050 Davis Aug. 28, 19342,042,145 Darrah May 26, 1936 2,231,457 Stephen Feb. 11, 1941 2,308,043Bierwirth Jan. 12, 1943 FOREIGN PATENTS Number Country Date 375,587Great Britain June 30, 1932

